In recent years, much research and development of MO recording media for use as high density/high capacity memory devices has been carried out. Such media typically comprise a suitable substrate, e.g., of glass, polymer, metal, or ceramic material, coated with a perpendicularly magnetizable film used as a recording medium. Information is recorded within the medium by switching the direction of magnetization of desired portions (i.e., domains) of the perpendicularly magnetizable film. More specifically, for recording information, the recording medium is first initialized by applying to the medium a magnetic field from an externally positioned magnetic field generation device (i.e., external magnetic bias), thereby making the direction of the perpendicular magnetization uniformly upwardly or downwardly facing. A first laser beam of sufficiently high power or intensity from a suitable source, e.g., a laser diode, is then irradiated on desired recording portions of the recording medium in the presence of an external biased magnetic field. As a consequence of the laser beam irradiation, the temperature of the irradiated portions (domains) of the recording medium rises, and when the temperature reaches or exceeds the Curie point of the vertically magnetizable film or its magnetic compensation point, the coercive force on the recording portion becomes zero or substantially zero. When this state is achieved at the desired recording portions of the medium, and in the presence of the externally biased magnetic field, the direction of the perpendicular magnetization is switched, e.g., from upwardly facing (=digital logic 1 or 0) to downwardly facing (=digital logic 0 or 1, respectively) and vice versa, so as to be aligned with that of the external magnetic field. At the end of a write pulse (i.e., laser pulse), the temperature of the heated recording domain then decreases and eventually returns to room temperature by ceasing laser beam irradiation thereof. Since the alignment direction of magnetization of the recording media effected by the laser pulse heating to above the Curie temperature is maintained at the lowered temperature, desired information can thus be recorded in the magneto-optical media.
For reading the information stored in the MO media according to the above-described method, the recorded portions of the media are irradiated with a second, linearly polarized laser beam of lower power or intensity than the one used for recording, and light reflected or transmitted from the recorded portions is detected, as by a suitable detector/sensor means. The recorded information is read out by detecting the Kerr rotation angle of the polarization plane of light reflected from the recording layer or the Faraday rotation angle of the polarization plane of light transmitted through the recording layer. More particularly, since the rotation angle of the polarization plane varies depending upon the direction of magnetization of the recorded portions of the media according to the Kerr or Faraday effect, information stored within the media can be read out optically by a differential detector which decodes the polarization-modulated light beam into bits of information.
Such MO recording media, when fabricated in disk form for rotation about a central axis, can be adapted for use in conventional Winchester, or hard drive, devices as are employed with conventional magnetic recording media. Hard drives typically employed for such disk-shaped media utilize flying heads for mounting transducer/sensor devices, etc., thereon, for close positioning thereof adjacent the surface of the recording media. In operation, a typical contact start/stop (CSS) method commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined small distance from the surface of the disk, where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Therefore, as in the case of magnetic disks, a lubricant (optionally with an underlying protective layer) is typically applied to the disk surface for minimizing scratching and abrasion of the sensor/transducer head and the recording media surface, which can result in an undesirably high wear rate of the head and recording media surface, as disclosed in, e.g., U.S. Pat. Nos. 5,386,400; 5,618,617; 5,578,355; 5,527,479; 5,112,662; and 5,604,005.
However, in the case of portable MO recording devices, the use of a lubricating oil, e.g., a fluorocarbon-based oil, is problematic in that it is difficult to maintain the lubricating oil on the surface of the MO media, thereby increasing surface scratching and wear. In addition, MO disks produced without lubricating oil on their surface by some manufacturers are not necessarily compatible with similar media produced with lubricating oil by other manufacturers.
In another approach for minimizing abrasion, scratching, and wear of transducer heads, a solid lubricant is applied to the bottom surface of the flying head which comes into contact with the surface of the MO recording medium. However, such solid lubricant applied to the bottom surface of the flying head must have a durability many times greater than lubricant applied to the MO recording medium. As a consequence, application of solid lubricant only to the flying head is not sufficient for adequately reducing abrasion, scratching, and wear.
An additional difficulty encountered in the development of wear-resistant, lubricated MO recording media and Winchester-type drives therefor, is the requirement imposed by the impetus for achieving ever-higher density recording, which necessitates further reduction in the disk-transducer/sensor spacing. The head-to-disk interface (HDI) becomes very critical as head-disk spacing is reduced and head fly height decreases. Conventional MO media without a protective overcoat and lubricant layer have extremely poor tribological performance, resulting in lack of reliability of MO-based disk drives.
Thus, there exists a need for a protective overcoat/lubricant topcoat layer system which enables the manufacture of reliable, very high density recording MO-based disk drives, which layer system effectively eliminates the problems and drawbacks associated with the conventional MO-based technology, i.e., scratching, abrasion, and increased wear of transducer/sensor head and recording media surfaces.
The present invention addresses and solves the problems attendant upon the use of conventional MO-based disk-shaped recording media and hard drives, while maintaining full compatibility with all mechanical aspects of conventional disk drive technology.